Algal cells are a promising source of biofuels (Wijffels & Barbosa (2010) Science 329:796-799). Their ability to harness solar energy to convert carbon dioxide into carbon-rich lipids already exceeds the abilities of oil-producing agricultural crops, with the added advantage that algae grown for biofuel do not compete with oil-producing crops for agricultural land (Wijffels & Barbosa, 2010). Parachlorella phytoplankton are unicellular green algae (phylum Chlorophya) of the Trebouxiophyceae class that can be cultured easily, rapidly, and economically. In order to maximize algal fuel production, new algal strains will need to be engineered for growth and carbon fixation at an industrial scale (Wijffels & Barbosa, 2010).
While it will be necessary to manipulate algal genomes, such as the Parachlorella genome, in order to maximize biofuel output, this has proven difficult to date because of the thick cell wall that surrounds many algal cells, including Parachlorella cells. In fact, to our knowledge, techniques for reliable and reproducible methods for transformation of Parachlorella cells have not been developed or published. There is a lack of knowledge relating to techniques suitable for transforming may species of algae, including algae of the Trebouxiophyceae class, such as Parachlorella cells, with transgenes. Consistent procedures for genetic manipulation of these organisms are needed.
Further, modern recombinant strain development requires robust and efficient tools for expressing transgenes to alter cellular metabolism and physiology in desired ways. An essential component of any genetic engineering “toolkit” is a suite of functional promoters to drive transgene-expression. There is a need for endogenous promoters, cloned and verified, from the strains for which recombinant DNA technology is being developed as well as additional strategies for increasing transformation of microorganisms such as algae and improved expression of heterologous genes.